Relief valve

ABSTRACT

A gap  11  between a flange  4 A of a ball support member  4  and the inner circumferential surface of a sleeve member  7  functions as an orifice for restricting an oil flow downstream of a seat hole ( 6 B). The movement of the ball support member  4  is stabilized, pressure is generated in a chamber  9  downstream of a seat hole  6 B, and the override characteristics of the relief valve  1  are improved.

FIELD OF THE INVENTION

[0001] This invention relates to a relief valve.

BACKGROUND OF THE INVENTION

[0002] JP-A-H8-42513 published in 1996 by the Japanese Patent Officediscloses a relief valve included in the flow control valve of a powersteering device.

[0003]FIG. 10 shows this flow control valve 200. A relief valve 250 isincorporated in a spool 201 of the flow control valve 200, as shown inthe diagram.

[0004] Oil supplied to a supply chamber 202 at the tip of the spool 201from the pump port P is supplied to the power steering device via anorifice 203 and an oil supply port 204.

[0005] The oil pressure on the side of the oil supply port 204 (oilpressure downstream of the orifice 203) is introduced to a flowratecontrol spring chamber 205 at the base end of the spool 201. The spool201 displaces under a balance between a thrust force due to the oilpressure of the supply chamber 202 and the supply port 204 (oil pressureboth upstream and downstream of the orifice 203), and a reaction due tothe spring force of a spring 206 provided in the flow rate controlspring chamber 205 and the oil pressure of the flowrate control springchamber 205. When the differential pressure upstream and downstream ofthe orifice 203 increases due to an increase of the pump rotation speed,the thrust force due to the oil pressure of the supply chamber 202exceeds the reaction force, the spool 201 displaces in the basedirection (left-hand direction of FIG. 10), and the supply chamber 202communicates with a tank port T. Therefore, part of the flowrate fromthe pump port P is returned to the tank, and the flowrate is controlled.

[0006] When the load on the power steering device increases and the oilpressure of the oil supply port 204 sharply increases, if the oilpressure of the pressure control spring chamber 205 exceeds the setpressure of the relief valve 250, the relief valve 250 is pushed open,and oil in the pressure control spring chamber 205 escapes to the tankport T. As a result, the spool 201 displaces in the base end direction,oil pressure in the supply chamber 202 escapes to the tank port T, andthe supply pressure is prevented from increasing beyond the permittedpressure.

SUMMARY OF THE INVENTION

[0007] However, in the aforesaid relief valve 250, there is a large gapbetween a ball support member 252 which supports a ball 251, and theinner circumference of a valve hole 253, so movable members (the ball251 and ball support member 252) easily vibrate in a side direction(radial direction) due to the effect of the inclination of a returnspring 254 and the side force of the flow when the relief valve 250opens.

[0008] Further, in this relief valve 250, in a transient state when themovable members are pushed open, noise is produced by chattering whichmakes the operation of the movable members unstable. If the diameter ofa seat orifice 255 is reduced, this chattering can be suppressed, but inthis case pressure losses increase, and override characteristics of therelief valve 250 (characteristics of the difference between a setpressure and a cracking pressure) are impaired. It is therefore anobject of this invention to stabilize the operation of movable members,prevent chattering and improve override characteristics in a reliefvalve.

[0009] In order to achieve the above object, this invention provides arelief valve, comprising a valve seat comprising a seat hole, a ballwhich opens and closes the seat hole from the downstream side, a movablemember which supports the ball from the downstream side, a housing partwhich houses the movable member, and an orifice formed downstream of theseat hole which damps the vibration of the movable member and suppresseschattering by restricting an oil flow.

[0010] According to an aspect of this invention, this invention providesa flowrate control valve which controls the flowrate supplied from apump to a load circuit comprising a relief valve, the relief valvecomprising a valve seat having a seat hole, a ball which opens andcloses the seat hole from the downstream side, a movable member whichsupports the ball from the downstream side, a housing part which housesthe movable member, and an orifice formed downstream of the seat holewhich damps the vibration of the movable member 4 and suppresseschattering by restricting an oil flow. The relief valve opens when thepressure on the load circuit side rises, and part of the fluid from thepump is discharged to a tank port.

[0011] The details as well as other features and advantages of thisinvention are set forth in the remainder of the specification and areshown in the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012]FIG. 1 is a cross-sectional diagram of a vane pump in which therelief valve of this invention is applied.

[0013]FIG. 2 is a cross-sectional view through a line A-A in FIG. 1.

[0014]FIG. 3 is a cross-sectional view of a flowrate control valve andrelief valve.

[0015]FIG. 4 is similar to FIG. 3, but showing a second embodiment ofthis invention.

[0016]FIG. 5A is a cross-sectional view of a relief valve according to athird embodiment of this invention.

[0017]FIG. 5B is a cross-sectional view through a line B-B in FIG. 5A.

[0018]FIG. 6A is a cross-sectional view of a relief valve according to afourth embodiment of this invention.

[0019]FIG. 6B is a cross-sectional view through a line C-C in FIG. 6A.

[0020]FIG. 7 is similar to FIG. 3, but showing a fifth embodiment ofthis invention.

[0021]FIG. 8 is similar to FIG. 3, but showing a sixth embodiment ofthis invention.

[0022]FIG. 9 is similar to FIG. 3, but showing a seventh embodiment ofthis invention.

[0023]FIG. 10 shows the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] In the following embodiments, the relief valve of this inventionis incorporated in a flowrate control valve which controls the oilflowrate to a power steering device from a vane pump.

[0025]FIG. 1, FIG. 2 show the construction of a vane pump 20. Theconstruction of the vane pump is common to each embodiment.

[0026] The vane pump 20 comprises a body 21, cover 22, shaft 23, rotor24, cam ring 25 and side plate 26.

[0027] The shaft 23 is a drive shaft of the rotor 24 installed in thebody 21, and is supported free to rotate in the body 21. The shaft 23 isconnected to the engine of a vehicle, not shown, and rotates togetherwith the rotation of the engine.

[0028] The rotor 24 is disposed on the inside of the cam ring 25 whichhas an elliptical inner wall. The rotor 24 is gripped between the cover22 and the side plate 26.

[0029] Plural vanes 27 are arranged radially on the outer circumferenceof the rotor 25. The vanes 27 can move into or out of the rotor 24. Whenthe rotor 24 rotates, the vanes 27 protrude until their ends come incontact with the inner circumferential surface of the cam ring 25. Dueto this, a pump chamber is formed between each of the vanes 27, thischamber expanding and contracting together with the rotation of therotor 24.

[0030] In the expansion stroke, these pump chambers draw in oil from alow pressure passage 28 which communicates with a tank, not shown. Onthe other hand, in the contraction stroke, oil is discharged into ahigh-pressure passage 29. The high-pressure passage 29 communicates withthe power steering device, not shown, via a flowrate control valve 30described later.

[0031]FIG. 3 shows the construction of the flowrate control valve 30according to the first embodiment of this invention, and a relief valve1 built into the flowrate control valve 30.

[0032] When the engine rotates at low speed, oil supplied to the powersteering device must increase together with increase of the enginerotation speed. On the other hand, when the engine rotates at highspeed, the amount of oil supplied to the power steering device must belimited so that it does not increase even if the engine rotation speedrises. The flowrate control valve 30 is provided for this flowratecontrol, and when the engine rotation speed (rotation speed of the vanepump 20) increases, it drains the oil which exceeds the required oilsupply amount.

[0033] The flowrate control valve 30 comprises a spool 40 housed free toslide in a slide hole 31 formed in the body 21 of the vane pump 20. Aconnector 32 is screwed into the open end of the slide hole 31. Thehollow part of the connector 32 is an oil supply port 32A for supplyingoil to the power steering device, not shown.

[0034] A plug 33 is fitted to the base of the connector 32. A hole isformed in the plug 33. A shaft member 41 of the spool 40 passes throughthis hole, and a gap between the outer circumference of the shaft member41 and the inner circumference of the hole forms an orifice 33A.

[0035] A large diameter part 41A and a small diameter part 41B having asmaller diameter than the large diameter part 41A, are formed in orderfrom the end at the shaft member 41 of the spool 40. Consequently, theopening area of the orifice 33A varies according to whether the largediameter part 41A or the small diameter part 41B is inside the hole.

[0036] In this embodiment, the opening area of the orifice 33A can bevaried by the shaft member 41 of the spool 40 in this way, but themember which varies the opening area of this orifice 33A may beseparated from the flowrate control valve 30, and the member whichvaries the opening area of the orifice 33A may be driven by a solenoid.In this way, the opening area of the orifice 33A can be controlled moreprecisely.

[0037] The oil supply port 32A (downstream of the orifice 33A)communicates with a flowrate control spring chamber 35 via acommunicating passage 37. An orifice 38 is provided between thecommunicating passage 37 and the oil supply port 32A, and an orifice 39is provided between the communicating passage 37 and flowrate controlspring chamber 35.

[0038] A contact step part 42 is formed at the base end of the shaftmember 41 of the spool 40. The diameter of the contact step part 42 islarger than the diameter of the opening of the plug 33. Hence, when thespool 40 displaces towards the tip end (left-hand side of the figure),and an end face 42A of the contact step part 42 comes in contact withthe plug 33, the orifice 33A is closed by the contact step part 42.

[0039] A sliding part (land part) 43 is formed at the base end of thecontact step part 42 of the spool 40. The sliding part 43 slides alongthe inner circumferential surface of the slide hole 31. The inside ofthe slide hole 31 is divided into a supply chamber 34 (upstream of theorifice 33A) at the tip end of the spool 40 (left-hand side of thefigure), and the flowrate control spring chamber 35 at the base end ofthe spool 40 (the right-hand side of the figure), by this sliding part43.

[0040] The base end from the sliding part 43 of the spool 40 is a baseend part 44 of smaller diameter than the sliding part 43. A flowratecontrol spring 36 is disposed on the outer circumference of this baseend part 44. The base end of the flowrate control spring 36 comes incontact with the base of the slide hole 31, and the flowrate controlspring 36 pushes the spool 40 in the direction of the tip end (left-handside of the figure).

[0041] A pressure port P which communicates with the high-pressurepassage 29 of the vane pump 20 and a tank port T which communicates witha tank, open onto the side face of the slide hole 31. The pump port P issituated near the open end of the slide hole 31, and communicates withthe supply chamber 34. The tank port T is situated on the far inside(right-hand side of the figure) of the slide hole from the pump port P,and communication and non-communication with the supply chamber 34, andthe communicating area when they do communicate, may be changed over bythe displacement of the spool 40.

[0042] The relief valve 1 is built into the spool 40 from the side ofthe flowrate control spring chamber 35. The relief valve 1 is used as apilot valve when pressure control is performed in the flowrate controlvalve 30. Specifically, when a large load acts on the power steeringdevice and the pressure of the oil supply port 32A sharply increases,the flowrate control valve 30 also functions as a pressure control valvewhich decreases the supply pressure from the vane pump 20. In thispressure control, the relief valve 1 is a valve which is built into thespool 40 of the flowrate control valve 30 functions as a valve whichcontrols the flowrate control valve 30 when the pressure of the oilsupply port 32A increases.

[0043] The relief valve 1 comprises a return spring 3, ball supportmember 4, ball 5, valve seat 6 and sleeve member 7 built into the valvehole 2 which opens onto the base end of the spool 40.

[0044] The sleeve member 7 is fixed to the inner circumferential surfaceat the open end of the valve hole 2. The valve seat 6 is fixed to aninner circumferential surface 7A of the sleeve member 7. A seat orifice6A is formed coaxially with the valve seat 6, and a downstream end partof this seat orifice 6A forms a seat hole 6B. A filter 8 is attached tothe open end (upstream of the seat orifice 6A) of the valve hole 2.

[0045] The ball 5 and ball support member 4 are disposed downstream ofthe valve seat 6 (left-hand side of FIG. 3). A return spring 3 isprovided on the outer circumference of the ball support member 4. Thereturn spring 3, disposed between a flange 4A of the ball support member4 and the base surface of the valve hole 2, pushes the ball supportmember 4 in the direction of the valve seat 6.

[0046] The ball 5 is supported by the ball support member 4, and ispushed against the seat hole 6B of the valve seat 6 by the spring forceof the return spring 3 so as to seal the seat hole 6B. When a fluidpressure in the flowrate control spring chamber 35 of the flowratecontrol valve 30 exceeds the spring pressure of the return spring 3, theball 5 is pushed open, and oil is introduced into the valve hole 2 fromthe seat orifice 6A and seat hole 6B.

[0047] The flange 4A is formed at the base end of the ball supportmember 4. The flange 4A divides the inside of the valve hole 2 into achamber 9 and a pressure control spring chamber 10.

[0048] A gap 11 is formed as an orifice between the flange 4A and theinner circumferential surface 7A of the sleeve member 7 which extends tothe side of the flange 4A. The gap 11 is a gap which is sufficientlynarrow to have a sufficient damping effect on the movement of the ballsupport member 4, and its width in the radial direction is preferablyset to below {fraction (1/20)} of the inner diameter of the sleevemember 7.

[0049] Due to this gap 11, in the relief valve 1, the movement of theball support member 4 and ball 5 can be stabilized without decreasingthe override characteristics, and the noise due to chattering can besuppressed. The fact that sufficient damping effect is obtained when thewidth (width in the radial direction) of the gap 11 is set to less than{fraction (1/20)} of the inner diameter of the sleeve member 7, isconfirmed by experiment and analysis.

[0050] The pressure control spring chamber 10 communicates with the tankport T via plural oil passages 12 and an outer circumferential groove13. The outer circumferential groove 13 is an annular groove formed onthe outer circumference of a slide part 43 of the spool 40.

[0051] Next, the operation of this device will be described.

[0052] When the engine, not shown, is started, the vane pump 20 rotatesaccording to the engine rotation, and oil is supplied to the supplychamber 34 of the flowrate control valve 30 from the pump port P. Thisoil flows into the oil supply port 32A via the orifice 33A, and issupplied to the power steering device. When the oil supply amountsupplied to the power steering device is small at low pump rotationspeeds, the oil supply amount increases in direct proportion to the pumprotation speed.

[0053] In this case, the differential pressure between the supplychamber 34 (upstream of the orifice 33A) and the oil supply port 32A(downstream of the orifice 33A) is determined by the opening area of theorifice 33A and the flowrate passing through the orifice 33A, and itincreases as the rotation speed of the vane pump 20 rises and theflowrate flowing through the orifice 33A increases.

[0054] Oil is led to the pressure control spring chamber 35 of theflowrate control valve 30 via the orifice 38, oil passage 37 and orifice39. When the rotation speed of the vane pump 20 increases and thedifferential pressure upstream and downstream of the orifice 33Aincreases, the spool 40 displaces in the base end direction (right-handside of the figure) against the flowrate control spring 36.Specifically, when the flowrate passing through the orifice 33Aincreases, a thrust force (product of a pressure P1 of the supplychamber 34 and pressure receiving area A1 on the side of the supplychamber 34 of the spool 40 and the axial force due to the pressure inthe oil supply port 32A) which presses the spool 40 in the base enddirection, exceeds the reaction (sum of the spring force F of theflowrate control spring 36, and product of the pressure P2 of theflowrate and control spring chamber 35 and pressure receiving area A2 onthe side of the flowrate control spring chamber 35 of the spool 40)which presses the spool 40 back towards the tip end (left-hand side ofthe figure), the spool 40 retreats in the base end direction.

[0055] Due to the retreat of the spool 40, the supply chamber 34communicates with the tank port T. Hence, part of the oil supplied fromthe pump port P is discharged to the tank port T, and increase of theoil supply amount supplied to the power steering device is suppressedeven if the pump rotation speed rises. Further, when the large diameterpart 41A of the spool 40 moves inside the orifice 33A, the opening areaof the orifice 33A becomes narrow, and the oil supply amount supplied tothe power steering device is further suppressed. In this way, the oilsupply amount to the power steering device is controlled according tothe pump rotation speed.

[0056] Also, the pressure of the supply chamber 34 is controlled asfollows. For example, when the pressure of the oil supply port 32Aincreases sharply due to a kickback or the like from the power steeringdevice, this pressure is transmitted to the flowrate control springchamber 35 via the orifice 38, oil passage 37 and orifice 39. Hence, thepressure of the flowrate control spring chamber 35 increases, and whenit exceeds the set pressure of the relief valve 1, the relief valve 1 ispushed open, and the flowrate control spring chamber 35 and tank port Tare made to communicate. Specifically, the ball 5 and ball supportmember 4 are pushed open against the spring force of the return spring3, and oil in the flowrate control spring chamber 35 is discharged tothe tank port T via the filter 8, the seat orifice 6A, the seat hole 6B,a chamber 9, the gap 11 which functions as an orifice, a pressurecontrol spring chamber 10, an oil passage 12 and the outercircumferential groove 13. As a result, the pressure of the flowratecontrol spring chamber 35 decreases, and the spool 40 retreats towardthe right of the figure. Hence, the supply pressure of the supplychamber 34 is discharged to the tank port T, and is controlled so thatit does not become excessive. Further, the opening area of the orifice33A is made narrower by the large diameter part 41A, and the flowrateflowing into the power steering device is limited.

[0057] The relief valve 1 functions in this way in pressure control, butaccording to this embodiment, the gap 11 is formed between the flange 4Aand the inner circumferential surface 7A of the sleeve member 7.Therefore, due to the resistance (pressure loss) and damping force whenoil passes through this gap 11, override is improved, the operation ofthe ball support member 4 is stabilized, and chattering is suppressed.Specifically, vibration of the ball support member 4 in the side andaxial directions is suppressed, and noise accompanying this vibration isprevented.

[0058] Also, due to the gap 11, a pressure appears in the chamber 9(downstream of the seat hole 6B of the relief valve 1) and the pressureincreases as the flowrate increases, so the override characteristics ofthe relief valve 1 (difference between the set pressure and crackingpressure of the relief valve 1) improve.

[0059]FIG. 4 shows a second embodiment.

[0060] The second embodiment is different from the first embodiment inthe following points.

[0061] The sleeve member 7 of the second embodiment is shorter than thatof the first embodiment, and it does not extend to the side of theflange 4A of the ball support member 4. Instead, a guide depression 62Ais formed in a valve hole 2 on the side of the flange 4A, and a gap 63between the flange 4A and guide depression 62A functions as an orifice.The gap 63 is sufficiently narrow to have a sufficient damping effect onthe movement (vibration) of the ball support member 4, and the width inthe radial direction is preferably set to less than {fraction (1/20)} ofthe inner diameter of the depression 62A.

[0062] Therefore, in addition to having an identical effect to that ofthe first embodiment, according to the second embodiment, there is noneed to adjust the relation between the inner diameter of the sleevemember 7 and the outer diameter of the flange 4A forming the gap 63, andfreedom of design is enhanced.

[0063] It is not absolutely necessary to provide the guide depression62A in the valve hole 2, and the gap 63 may be formed between theflange4A and the inner circumferential surface of the valve hole 2 whichdoes not have a depression.

[0064]FIG. 5A shows the relief valve 1 according to a third embodiment.FIG. 5B shows a cross-sectional view through a line B-B in FIG. 5A.

[0065] The third embodiment is different from the first embodiment inthe following points. Also in the third embodiment, the relief valve 1is built into the spool 40 of the flowrate control valve 30 as in thecase of the aforesaid first embodiment.

[0066] In the third embodiment, the flange 4A of the ball support member4 is made wider in the axial direction, and its outer circumferentialsurfaces slides on the inner circumferential surface 7A of the sleevemember 7. Plural grooves 73 (in this embodiment, four notches providedat 90 degree intervals) are formed extending in the axial direction ofthe ball support member 4, and these grooves 73 function as orifices.The grooves 73 are set to a width and depth at which sufficient dampingeffect can be exerted on the movement (vibration) of the ball supportmember 4.

[0067] Due to these grooves 73, in the third embodiment, an identicaleffect is obtained as in the case of the first embodiment. The flange 4Acomes in contact with the inner circumferential surface 7A of the sleevemember 7, so vibration of the ball support member 4 in the sidedirection is completely prevented. According to this embodiment, thegrooves 73 are formed by cutting notches out of the outercircumferential surface of the flange 4A, so they are easily formed,precise machining is easy, and precision of the damping force setting isenhanced. Further, as the grooves 73 are formed on the outercircumferential surface of the flange 4A, they are not sealed off by theedges of the return spring 3. In this embodiment, the grooves 73 areformed in the outer circumference of the flange 4A, but they may beformed in the inner circumference 7A of the sleeve member 7.

[0068]FIG. 6A shows a fourth embodiment. FIG. 6B shows a verticalcross-sectional through a line C-C of FIG. 6A.

[0069] The fourth embodiment differs from the first embodiment in thefollowing points. Also in the fourth embodiment, the relief valve 1 isbuilt into the spool 40 of the flowrate control valve 30.

[0070] According to the fourth embodiment, the flange 4A of the ballsupport member 4 is made wider in the axial direction, and its outercircumferential surfaces slides completely on the inner circumferentialsurface 7A of the sleeve member 7. Plural depressions 83 which open ontothe pressure control spring chamber 10 are formed in the outercircumferential surface of the flange 4A. Further, holes 84 whichaxially pass through the flange 4A are provided in the inner part of thedepressions 83. These throughholes 84 function as orifices. Thecross-sectional areas of the throughholes 84 are set to a size such thata sufficient damping effect on the movement (vibration) of the ballsupport member 4 is obtained.

[0071] Due to the throughholes 84, an identical effect is obtained inthe fourth embodiment as in the first embodiment. Further, the flange 4Acomes in contact with the inner circumferential surface 7A of the sleevemember 7, so vibration of the ball support member 4 in the sidedirection is completely prevented. The orifice is formed as thethroughholes 84 which pass through the flange 4A, so it can be easilyformed, precise machining is easy, and the precision of the dampingforce setting is enhanced. Further, the throughholes 84 are formedinside the depression parts 83, so even if the return spring 3 isinstalled at the end of the flange 4, they are not sealed off by the endof the return spring 3.

[0072]FIG. 7 shows a fifth embodiment.

[0073] The fifth embodiment differs from the first embodiment in thefollowing points. The remaining features of the construction areidentical.

[0074] In the fifth embodiment, the pressure control spring chamber 10and outer circumferential groove 13 communicate not through the oilpassage 12 but through an orifice 93.

[0075] When the relief valve 1 is pushed open, due to the flow throughthe orifice 93, a suitable back pressure is set up in the pressurecontrol spring chamber 10, the effect of mixing with air is suppressed,and cavitation in the pressure control spring chamber 10 is prevented.The operation of the ball support member 4 is stabilized, and noise dueto chattering is reduced. Further, a pressure appears in the chamber 9downstream of the seat hole 6B, so override characteristics areimproved.

[0076]FIG. 8 shows a sixth embodiment.

[0077] In the sixth embodiment, in the construction of the fifthembodiment (FIG. 7) wherein the pressure control valve chamber 10 andthe outer circumferential groove 13 communicate via an orifice, anotch-shaped orifice 103 is formed on the outer circumference of theflange 4A.

[0078] Specifically, in the sixth embodiment, the flange 4A of the ballsupport member 4 slides on the inner circumferential surface 7A of thesleeve member 7, and the notch-shaped orifice 103 is formed on the outercircumference of the flange 4A. The cross-sectional area of the orifice103 is set to a size such that a sufficient damping effect is given tothe movement (vibration) of the ball support member 4.

[0079] The pressure control valve chamber 10 and outer circumferentialgroove 13 communicate via an orifice 104. Due to this construction,vibration of the ball support member 4 in the side direction is moredefinitely prevented.

[0080]FIG. 9 shows a seventh embodiment.

[0081] In the seventh embodiment, the construction of the relief valve 1is identical to that of the first embodiment, however the opening areaof an orifice 118 between the pump port P and an oil supply port 120which supplies oil to the power steering device is made variable by asolenoid valve 110, unlike the first embodiment.

[0082] The spool 40 of the flowrate control valve 20 comprises an endpart 46 of small diameter situated at the end of the sliding part 43which slides in the slide hole 31. The pump port P opens onto the sideof this end part 46. The tank port T opens onto the side of the slidepart 43, and opens onto the end part 46 when the spool 14 has retractedso that part of the fluid from the pump port P is discharged to the tankport T.

[0083] The solenoid valve 110 is disposed between the oil supply port120 which communicates with the power steering device, and the pump portP. The solenoid valve 110 comprises a fixed iron core 112 which has acoil 111 on the outer circumference, and a rod 114 which has a movableiron core on the outer circumference. The rod 114 is supported free toslide in an axial direction via bearings 115, 116, and is driven byenergizing the coil 111. The end part of the rod 114 engages with theopening of a seat 117. The outer circumferential part of this rod 114and the seat 117 form an orifice 118, the opening area of the orifice118 being varied by the retraction of the rod 114.

[0084] Due to this construction, control of the opening area of theorifice 118 between the pump port P and oil supply port 120 can beperformed more precisely.

[0085] The aforesaid embodiments may be combined, and any desiredcombination may be used if it is possible.

[0086] The orifice downstream of the seat hole of the relief valve maybe provided in another way.

[0087] In the above embodiments, the relief valve was applied to aflowrate control valve of a vane pump supplying oil pressure to thepower steering device, but the invention is not limited to thisarrangement, and may be applied to a relief valve used for anyapplication.

[0088] The embodiments of this invention in which an exclusive propertyor privilege is claimed are defined as follows:

What is claimed is:
 1. A relief valve, comprising: a valve seatcomprising a seat hole; a ball which opens and closes the seat hole fromthe downstream side; a movable member which supports the ball from thedownstream side; a housing part which houses the movable member; and anorifice formed downstream of the seat hole which damps the vibration ofthe movable member and suppresses chattering by restricting an oil flow.2. The relief valve as defined in claim 1, wherein the orifice is a gapbetween the movable member and the inner circumferential surface of thehousing part.
 3. The relief valve as defined in claim 2, wherein: themovable member further comprises a flange of circular cross-section; theorifice is a gap between the flange and the inner circumferentialsurface of the housing part; and the width of the gap in the radialdirection is less than {fraction (1/20)} of the inner diameter of thehousing part.
 4. The relief valve as defined in claim 1, wherein: themovable member slides on the inner circumferential surface of thehousing part; and the orifice is grooves formed on either one of theouter circumferential surface of the movable member, and the innercircumferential surface of the housing part.
 5. The relief valve asdefined in claim 1, wherein: the movable member slides on the innercircumferential surface of the housing part; and the orifice is athroughhole through which the movable member passes.
 6. The relief valveas defined in claim 5, wherein the relief valve comprises a returnspring disposed on the movable member; depressions are formed in themovable member on the side where the return spring is installed; and thethroughhole opens onto the depressions.
 7. The relief valve as definedin claim 1, further comprising: a return spring disposed on the movablemember; a spring chamber housing the return spring downstream of theseat hole; and a second orifice between the spring chamber and a tankport.
 8. The relief valve as defined in claim 1, further comprising: athird orifice upstream of the seat hole.
 9. A flowrate control valvewhich controls the flowrate supplied from a pump to a load circuitcomprising a relief valve, the relief valve comprising: a valve seathaving a seat hole; a ball which opens and closes the seat hole from thedownstream side; a movable member which supports the ball from thedownstream side; a housing part which houses the movable member; and anorifice formed downstream of the seat hole which damps the vibration ofthe movable member 4 and suppresses chattering by restricting an oilflow, wherein: the relief valve opens when the pressure on the loadcircuit side rises, and part of the fluid from the pump is discharged toa tank port.
 10. The flowrate control valve as defined in claim 9,wherein the orifice is a gap between the movable member and the innercircumferential surface of the housing part.
 11. The flowrate controlvalve as defined in claim 10, wherein: the movable member furthercomprises a flange of circular cross-section; the orifice is a gapbetween the flange and the inner circumferential surface of the housingpart; and the width of the gap in the radial direction is less than{fraction (1/20)} of the inner diameter of the housing part.
 12. Theflowrate control valve as defined in claim 9, wherein: the movablemember slides on the inner circumferential surface of the housing part;and the orifice is grooves formed on either one of the outercircumferential surface of the movable member, and the innercircumferential surface of the housing part.
 13. The flowrate controlvalve as defined in claim 9, wherein: the movable member slides on theinner circumferential surface of the housing part; and the orifice is athroughhole through which the movable member passes.
 14. The flowratecontrol valve as defined in claim 13, wherein the relief valve comprisesa return spring disposed on the movable member; a depression is formedin the movable member on the side where the return spring is installed;and the throughhole opens onto the depression.
 15. The flowrate controlvalve as defined in claim 9, further comprising: a return springdisposed in the movable member; a spring chamber housing the returnspring downstream of the seat hole, and a second orifice between thespring chamber and the tank port.
 16. The flowrate control valve asdefined in claim 9, further comprising: a third orifice upstream of theseat hole.
 17. The flowrate control valve as defined in any of claims 9through 16, comprising: a spool; a supply chamber formed on one side ofthe spool; a flowrate control valve chamber formed on the other side ofthe spool; and a flowrate control spring provided in the flowratecontrol spring chamber which pushes the spool in the direction of thesupply chamber, wherein: a pump pressure is led to the supply chamber;oil is supplied from the supply chamber to a supply port to the loadcircuit via a supply orifice; the pressure downstream of the supplyorifice is led to the flowrate control valve chamber via at least oneorifice or throat, when the spool retracts in the direction of theflowrate control spring chamber, the supply chamber communicates withthe tank port, the relief valve is built into the spool from the side ofthe flowrate control spring chamber, and when the relief valve opens,the flowrate control spring chamber communicates with the tank port.